For future wearables, the network could be you

People who wear networked gadgets all over their bodies may someday become networks themselves.

Researchers at the University of California, San Diego, have found a way for wearables to communicate through a person's body instead of the air around it. Their work could lead to devices that last longer on smaller batteries and don't give away secrets as easily as today's systems do.

The proliferation of smartphones, smart watches, health monitoring devices and other gear carried close to the body has led to so-called personal area networks that link the gadgets together and provide a path to the Internet through one that has a Wi-Fi or cell radio. Today, those PANs use short-range over-the-air systems like Bluetooth.

But radio technologies like Bluetooth can't transmit well through the body itself, so they have to go around it. Bluetooth signals can travel as far as 10 meters (30 feet) which increases the chance of eavesdropping and leads to high "path loss," an effect that weakens signals on the way to their destinations, the researchers said.

A team led by Professor Patrick Mercier of the university's Department of Electrical and Computer Engineering has discovered a way to use the body itself as the medium for data transmission. It uses magnetic fields and shows path loss that's 10 million times lower than what happens with Bluetooth.

This could make the magnetic networks much more efficient, so devices don't have to work as hard to communicate and can have smaller batteries -- or get longer useful lives with the same size batteries. The team hasn't actually tested the system's energy use yet. They envision the technology being used for networks of health sensors that monitor many parts of the body.

Wireless technologies like Bluetooth radiate electrical and magnetic waves, which a human body tends to absorb, Mercier said. By contrast, his team's network transmits data over magnetic fields that are created between two coils. Those fields can easily travel through the body. The system works like NFC (near-field communications), but at a slightly longer range. It uses very low frequencies, in the range of 10MHz to 30MHz, and it can carry at least 1M bps (bit per second), enough for dedicated devices like sensors, he said.

There's just one catch: Anything that goes on the network needs to be circular and wrap around a part of the body. So smartwatches or fitness bands could work, but a sensor attached to the user's chest would need to be attached to a band around the chest.

The team built a prototype network and installed it on the body of Jiwoong Park, a Ph.D student in Mercier's lab, as a proof of concept. It used coils of insulated copper wire wrapped around each of his arms. The coils sent magnetic signals from one arm to another using his body as a guide.

There's no serious danger to the wearer's health because the magnetic fields are so weak, the researchers said. They're far weaker than those used by a device like an MRI (magnetic resonance imaging) machine or even the effect of the Earth's magnetic field on the body, Mercier said.

Though some signals may radiate out from the wearer's body, they dissipate quickly so there's not much chance of interception from nearby, Mercier said. Still, any medical data that sensors sent over the network would have to be encrypted, he added. Signals would probably flow into the body of someone that the wearer touched, but the researchers haven't tested that yet.

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